(1) Field of the Invention
The present invention relates to a system and method for controlling fuel injection quantities applicable to an internal combustion engine. The present invention particularly relates to the system and method for controlling a corrected fuel injection quantity at a time when the engine is accelerated irrespective of a synchronization injection of fuel executed in synchronization with an engine revolution.
(2) Background of the art
A fuel supply controlling system which executes injection of fuel whenever there is a request of acceleration of a vehicle through an engine irrespective of engine revolutions to improve a driveability of the vehicle during the acceleration. (Refer to page 113 of Vol. 35, No. 1 of automotive engineering published by a Tetsudo Nippon Sha on January, 1986.)
In the above-described fuel supply controlling system, since the fuel is to be supplied in a fastest response to the request of the acceleration, the fuel injection is to be executed immediately when there is the request of acceleration of the vehicle without waiting for the timing at which the synchronization injection is executed.
Such an injection method as described above is called an interrupt injection during the acceleration since the injection interrupts the normal synchronization injection of fuel. This is also simply referred to as an interrupt injection.
For example, when an iding contact of a throttle switch associated with a throttle valve is turned from an on state to an off state or a change rate of a basic pulsewidth Tp (=K.times.Q.sub.a / N, wherein K denotes a constant, Q.sub.a denotes an intake air quantity, and N denotes a number of engine revolutions per unit time) per time exceeds a reference level, the interrupt injection is executed. The injection of the former is called an off idle interrupt and the latter injection is called T.sub.p change rate interrupt injection.
A fuel quantity of the interrupt injection is set according to a driving condition during the determination of acceleration (e.g., the engine revolutions N and engine coolant temperature T.sub.w).
Since the interrupt injection has an object to obtain an output increase in the engine according to the acceleration request, the quantity of fuel supply is desirably a value derived according to an output variable of the engine.
However, since the interrupt quantity of fuel derived from the above-described system is calculated from the engine revolution numbers N and coolant temperature T.sub.w by referring to a table having parameters of the engine revolution speed and engine coolant temperature, the output increase of the engine due to the interrupt injection does not always exactly correspond to the desired engine output increase. Although the same interrupt injection quantity is to be supplied, the actual fuel quantity supplied in each cylinder becomes different due to the presence of insufficient flow within an injection valve(s) and/or of dirt adhered onto an intake air passage. In addition, a combustion pressure becomes different as a cylinder cooling efficiency becomes different even though the same fuel injection quantity is sucked from the injection valve into each cylinder. Hence, only the actual combustion of fuel reveals whether a previously set output of the engine is achieved.
To cope with different characteristics of the engine, the control is fedback and a target value of a controlled variable should be a variable corresponding to the output of the engine, for example, an indicated mean effective pressure P.sub.i.